Exhaust diffuser for a gas turbine engine exhaust system

ABSTRACT

An exhaust diffuser for a gas turbine engine includes a diffuser inlet, a diffuser exit, an inner diffuser wall, and an outer diffuser wall. The inner diffuser wall may include a first tubular member with a flared downstream portion. The outer diffuser wall may include a second tubular member at least partially about the inner diffuser wall and with a second flared downstream portion. The outer diffuser wall and the inner diffuser wall extend between the diffuser inlet and the diffuser exit, and form a diffusing flowpath therebetween. The second flared downstream portion may include a lower section and an upper section, with the upper section extending further downstream in an axial direction than the lower section, relative to the diffuser axis.

TECHNICAL FIELD

The present disclosure generally pertains to a gas turbine engines, and is more particularly directed toward an exhaust system for a gas turbine including exhaust diffuser.

BACKGROUND

A gas turbine engine generates high-temperature high-velocity exhaust gas. The exhaust diffuser is defined by an increase in flow area resulting in a reduction in the velocity of the exhaust flow which, in turn, leads to an increase in static pressure along its flow path. Because of this pressure recovery in the diffuser, the inlet-to-exit pressure ratio of the turbine is increased, resulting in an increase in both output power and thermal efficiency. Additionally, the exhaust system serves to redirect the exhaust gases away from downstream equipment or towards site-specific interfaces.

U.S. Pat. No. 5,257,906 issued to Gray, et al. on Nov. 5, 1993 shows an exhaust system for a steam turbine. In particular, the disclosure of Gray, et al. is directed toward an exhaust system having a diffuser that directs the flow of working fluid from a turbine exit to an exhaust housing having a bottom opening, thereby turning the flow 90 degrees from the axial to radial direction. In the exhaust housing, the flow exiting at the top of the diffuser turns 180 degrees from the vertically upward direction to the downward direction. The strength of the vortex formed in the exhaust housing as a result of this turning is minimized by orienting the outlet of an outer exhaust flow guide portion of the diffuser so that it lies in a plane that makes an angle with a plane perpendicular to the turbine axis. As a result, the minimum axial length of the outer flow guide occurs at a location remote from the exhaust housing outlet and the maximum axial length occurs at a location proximate the opening, thereby crowding the vortex against a radially extending baffle in the exhaust housing.

The present disclosure is directed toward overcoming known problems and/or problems discovered by the inventors.

SUMMARY

An exhaust diffuser for a gas turbine engine includes a diffuser inlet, a diffuser exit, an inner diffuser wall, and an outer diffuser wall. The inner diffuser wall may include a first tubular member with a flared downstream portion. The outer diffuser wall may include a second tubular member at least partially about the inner diffuser wall and with a second flared downstream portion. The outer diffuser wall and the inner diffuser wall extend between the diffuser inlet and the diffuser exit, and form a diffusing flowpath therebetween. The second flared downstream portion may include a lower section and an upper section, with the upper section extending further downstream in an axial direction than the lower section, relative to the diffuser axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.

FIG. 2 is an isometric view of an exhaust system of the gas turbine engine of FIG. 1.

FIG. 3 is a cutaway side view of the exhaust system of FIG. 2.

DETAILED DESCRIPTION

Systems and methods disclosed herein include an exhaust system for a gas turbine including an axial-to-radial exhaust diffuser and a radial exhaust collector downstream of the diffuser. Embodiments include an axial-to-radial exhaust diffuser wherein the diffuser exit is cutback.

FIG. 1 is a schematic illustration of an exemplary industrial gas turbine engine. Some of the surfaces have been left out or exaggerated (here and in other figures) for clarity and ease of explanation. Also, the disclosure will generally reference a center axis 95 of rotation of the gas turbine engine, which may be generally defined by the longitudinal axis of its shaft 120 (supported by a plurality of bearing assemblies 150). The center axis 95 may be common to or shared with various other engine concentric components. All references to radial, axial, and circumferential directions and measures refer to center axis 95, unless specified otherwise, and terms such as “inner” and “outer” generally indicate a lesser or greater radial distance from, wherein a radial 96 may be in any direction perpendicular and radiating outward from center axis 95.

In addition, the disclosure may reference a “forward” and an “aft” direction. Generally, all references to “forward” and “aft” are associated with the flow direction of primary air (i.e., air used in the combustion process), unless specified otherwise. For example, forward is “upstream” relative to primary air flow (i.e., towards the point where air enters the system), and aft is “downstream” relative to primary air flow (i.e., towards the point where air leaves the system).

Generally, a gas turbine engine 100 includes an inlet 110, a compressor 200, a combustor 300, a turbine 400, an exhaust system 500, and a power output coupling 600. The compressor 200 includes one or more compressor rotor assemblies 220. The combustor 300 includes one or more injectors 350 and includes one or more combustion chambers 390. The turbine 400 includes one or more turbine rotor assemblies 420. The exhaust system 500 includes an exhaust diffuser 520 and an exhaust collector 550.

In operation, air 10 enters the inlet 110 as a “working fluid”, and is compressed by the compressor 200. In the compressor 200, the working fluid is compressed in an annular flow path by a series of compressor rotor assemblies 220. Once compressed, the compressed air leaves the compressor 200 and enters the combustor 300, where it is diffused and fuel is added. The fuel and the compressed air are injected into the combustion chamber 390 via the injectors 350 and ignited. After the combustion reaction, energy is extracted from the combusted fuel/air mixture via the turbine 400 by a series of the turbine rotor assemblies 420. Exhaust gas 90 is then diffused in exhaust diffuser 520. The exhaust collector 550 collects, redirects, and releases the exhaust gas 90 from the system. Exhaust gas 90 may also be further processed (e.g., to reduce harmful emissions, and/or to recover heat from the exhaust gas 90).

One or more of the above components (or their subcomponents) may be made from stainless steel and/or durable, high temperature materials known as “superalloys”. A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys may include materials such as HASTELLOY, INCONEL, WASPALOY, RENE alloys, HAYNES alloys, INCOLOY, MP98T, TMS alloys, CMSX single crystal alloys, Alloy X, Alloy 188/230, and the like.

FIG. 2 is an isometric view of an exhaust system of the gas turbine engine of FIG. 1. In particular, this view is generally looking forward and upstream but in isolation from the rest of gas turbine engine 100. For clarity and illustration purposes, certain features/components have been added, removed, and/or modified. For example, in this view, an aft wall 554 of the exhaust collector 550 is only partially shown.

FIG. 3 is a cutaway side view of the exhaust system of FIG. 2. In particular, the side view coincides with a flow symmetry plane. The symmetry plane is formed by the center axis 95 and a discharge direction 559. For clarity and illustration purposes, certain features/components have been added, removed, and/or illustrated schematically. For example, in this view, components internal to the inner diffuser wall 523 (e.g., shaft 120 and bearings 150) are illustrated schematically with additional components removed.

As illustrated in FIG. 2 and FIG. 3, the exhaust diffuser 520 is an axial radial diffuser configured to pneumatically couple with and form a flowpath between the turbine 400 (FIG. 1) and the exhaust collector 550. In general, the exhaust diffuser 520 may be conceptualized as two concentric structures (e.g., tubes) having a diffuser axis 535, joined to each other via a plurality of struts 525 circumferentially distributed around the diffuser axis 535. The diffuser axis 535 may coincide with the center axis 95 when the exhaust diffuser 520 is installed onto the gas turbine engine 100. Accordingly, when installed, the flowpath may be an annular exhaust flow path between the turbine 400 and the exhaust collector 550, interrupted by only the struts 525 themselves. For convenience, the center axis 95 will be referred hereinafter to include the diffuser axis 535.

The exhaust diffuser 520 includes a diffuser inlet 521, a diffuser exit 522, an inner diffuser wall 523, and an outer diffuser wall 524. The exhaust diffuser 520 is configured to receive exhaust gas 90 in a generally axial direction from the turbine 400 via the diffuser inlet 521. The exhaust diffuser 520 is further configured to discharge the exhaust gas 90 in a generally radial direction into of the exhaust collector 550 via the diffuser exit 522.

The inner diffuser wall 523 and the outer diffuser wall 524 are generally tubular members circumscribing the center axis 95. The inner diffuser wall 523 includes a first flared downstream portion 541 proximate the diffuser exit 522 that extends radially outward. Similarly, the outer diffuser wall 524 includes a second flared downstream portion 543 proximate the diffuser exit 522 that extends radially outward.

At an upstream end, the inner diffuser wall 523 is positioned radially within the outer diffuser wall 524. At a downstream end, the inner diffuser wall 523 extends axially beyond the outer diffuser wall 524. The inner diffuser wall 523 and the outer diffuser wall 524 may be joined together by the plurality of struts 525 extending therebetween. According to one embodiment, the inner diffuser wall 523 and the outer diffuser wall 524 may be at least partially concentric.

Together, the inner diffuser wall 523 and the outer diffuser wall 524 form the diffuser inlet 521 and the diffuser exit 522. In particular, the diffuser inlet 521 may be an annular opening formed by concentric upstream ends of the inner diffuser wall 523 and the outer diffuser wall 524. Similarly, the diffuser exit 522 may be a circumferential band opening formed by an axial displacement of first flared downstream portion 541 and second flared downstream portion 543. According to one embodiment, the diffuser inlet 521 and the diffuser exit 522 may be interrupted or traversed by members extending between the inner diffuser wall 523 and the outer diffuser wall 524 (e.g., struts, vanes, etc.).

Together, the inner diffuser wall 523 and the outer diffuser wall 524 also form the flowpath between the turbine 400 and the exhaust collector 550. In particular, an outer surface of the inner diffuser wall 523 and an inner surface of the outer diffuser wall 524 form an annular flowpath between the turbine 400 and the exhaust collector 550. As the flowpath advances downstream it transitions from a predominantly annular shape to a predominantly circumferential band shape directed radially outward. According to one embodiment, the flowpath may be interrupted or traversed by members extending between the inner diffuser wall 523 and the outer diffuser wall 524 (e.g., struts, vanes, etc.).

Additionally, an inner surface of the inner diffuser wall 523 and an outer surface of the outer diffuser wall 524 may differ in shape from their opposing sides (discussed above). For example, both the inner surface of the inner diffuser wall 523 and the outer surface of the outer diffuser wall 524 may have a generally cylindrical shape or a stepped cylindrical shape (each step having a different diameter). Alternately, portions of both the inner surface of the inner diffuser wall 523 and the outer surface of the outer diffuser wall 524 may be cylindrical or stepped, and other portions may be shaped similar to their respective opposing sides. Note, hereinafter, discussion of the inner diffuser wall 523 and the outer diffuser wall 524 refers to the flowpath surfaces (i.e., the outer surface of the inner diffuser wall 523 and the inner surface of the outer diffuser wall 524) unless specifically described otherwise.

As illustrated, the exhaust collector 550 is a radial exhaust collector configured to pneumatically couple with the exhaust diffuser 520, “collect” the exhaust gas 90 and redirect it radially away in a single, convenient discharge direction 559 away from the gas turbine engine 100 (FIG. 1). In one embodiment, the exhaust collector 550 is an enclosure wrapping around the exhaust diffuser 520 and having a single opening in a generally radial direction for discharge of the exhaust gas 90. Here, the exhaust collector 550 is configured to radially receive the exhaust gas 90 and redirect it radially upward, or along a discharge direction 559 of approximately 0 degrees or +/−5 degrees from top dead center (TDC), without an axial component.

The exhaust collector 550 includes an exhaust collector exit 551, a forward wall 552, a circumferential wall 553, and the aft wall 554. The exhaust collector 550 is configured to receive exhaust gas 90 in a generally radial direction from the exhaust diffuser 520 via the diffuser exit 522. The exhaust collector 550 is further configured to discharge the exhaust gas 90 in the discharge direction 559 away from the gas turbine engine 100 via the exhaust collector exit 551.

Together, the forward wall 552, the circumferential wall 553, and the aft wall 554 enclose the diffuser exit 522 such that discharged exhaust gas 90 is directed to the exhaust collector exit 551. In particular, the circumferential wall 553 may encircle a majority of the diffuser exit 522, about the center axis 95, and be sufficiently offset to accept flow from the diffuser exit 522. In addition, the circumferential wall 553 may be bound on a forward side by the forward wall 552 and on an aft side by the aft wall 554.

Furthermore, the forward wall 552 and the aft wall 554 may each extend radially inward from the circumferential wall 553 and mate with the outer diffuser wall 524 and the inner diffuser wall 523, respectively, and/or any intervening member. According to one embodiment, the forward wall 552 may be a vertical wall coupled to the outer diffuser wall 524 forward of the diffuser exit 522, and the aft wall 554 may be a vertical wall coupled to the inner diffuser wall 523 aft of the diffuser exit 522.

Together, the forward wall 552, the circumferential wall 553, and the aft wall 554 form the exhaust collector exit 551. In particular, the exhaust collector exit 551 may be an opening formed by upstream ends of the forward wall 552, the circumferential wall 553, and the aft wall 554. For example, the upstream ends of the forward wall 552, the circumferential wall 553, and the aft wall 554 may be joined, forming a single path to exit the enclosure. The exhaust collector exit 551 may be of any convenient shape and orientation to the discharge direction 559. For example and as illustrated, the exhaust collector exit 551 may have a generally rectangular shape that is normal to the discharge direction 559.

According to one embodiment, the exhaust collector exit 551 may include one or more transition members configured to interface the exhaust collector 550 with additional exhaust ducting. In particular, the one or more transition members may mate with both the exhaust collector 550 (having a first shape and/or effective flow area) and additional exhaust ducting (having a second, dissimilar shape and/or effective flow area), transitioning between the two. For example, the exhaust collector exit 551 may include a hood configured to couple to the exhaust collector exit 551 in a generally rectangular shape and first effective flow area, and transition to a round exhaust duct having a second effective flow area. Also for example, the one or more transition members may interface with the exhaust collector exit 551 and/or additional exhaust ducting at oblique angles, irregular or asymmetrical shapes, or as otherwise convenient.

Although the exhaust collector 550 is configured here to discharge the exhaust gas 90 upward, the exhaust collector 550 may be configured to discharge the exhaust gas 90 along other discharge directions 559. For example, the exhaust collector 550 may be configured to discharge the exhaust gas 90 radially sideways, or along a discharge direction 559 of approximately +/−90 degrees from TDC without an axial component. Also for example, the exhaust collector 550 may be configured to discharge the exhaust gas 90 along any discharge direction 559 between +90 degrees and −90 degrees from TDC, without an axial component. According to another embodiment, the exhaust collector 550 may be configured to discharge the exhaust gas 90 along any discharge direction 559 between +135 degrees and −135 degrees from TDC without an axial component. Alternately, the exhaust collector 550 may be configured to discharge the exhaust gas 90 along any of the abovementioned discharge directions 559 or ranges of discharge directions 559, but with an axial component up to 45 degrees aft.

The exhaust diffuser 520 may be mounted to the turbine 400 and configured to axially receive exhaust gas 90 leaving the turbine 400 in a predominantly axial flow 531. As illustrated, the predominantly axial flow 531 may have a velocity vector between +/−15 degrees, relative to the center axis 95, but no greater than +/−45 degrees, relative to the center axis 95. The exhaust diffuser 520 may be further configured to diffuse the exhaust gas 90, impart a radial component to its flow, and radially discharge the exhaust gas 90 as a predominantly radial flow 532 around the center axis 95 and into the exhaust collector 550. As illustrated, the predominantly radial flow 532 may have a velocity vector between 75 degrees and 105 degrees, relative to the center axis 95, but no less than 45 degrees and no greater than 135 degrees, relative to the center axis 95.

The exhaust collector 550 may be mounted to the exhaust diffuser 520 and/or any other supporting structure. The exhaust collector 550 may be configured to receive exhaust gas 90 expelled from the diffuser exit 522 and redirect it around and toward the exhaust collector exit 551, and expel the exhaust gas 90 in the discharge direction 559.

The exhaust diffuser 520 may include a linear diffusion region 526 followed by a turning region 527. The linear diffusion region 526 be shaped as an annular conical frustum, or the like, configured to increase the effective flow area between the inner diffuser wall 523 and the outer diffuser wall 524 from the diffuser inlet 521 to turning region 527. In particular, the effective flow area may increase relative to the operation conditions of the exhaust gas 90 so as to increase recovery and inhibit separation. For example, the effective flow area may be increased along the flowpath by increasing the distance between the diffuser inlet 521 and the diffuser exit 522 with respect to the flowpath. Also for example, the effective flow area may be increased along the flowpath by increasing the average circumference of the flowpath.

According to one embodiment, linear diffusion region 526 may include a canted flowpath. In particular, the inner diffuser wall 523 may form a conical frustum about the center axis 95. For example, the inner diffuser wall 523 may be angled between 0 degrees to 15 degrees away from the center axis 95 in the downstream direction. Also for example, the inner diffuser wall 523 may be angled between 3 degrees to 10 degrees away from the center axis 95 in the downstream direction. Also for example, the inner diffuser wall 523 may be angled approximately 5 degrees away from the center axis 95 in the downstream direction.

The turning region 527 is a curved region beginning at the linear diffusion region 526 and terminating downstream at the diffuser exit 522. The turning region 527 is configured to add a radial component to the velocity vector of the exhaust gas 90 and turn the exhaust gas 90 from the predominantly axial flow 531 to the predominantly radial flow 532.

The linear diffusion region 526 and the turning region 527 may include separable axial sections of the inner diffuser wall 523 and the outer diffuser wall 524. In particular, portions of the inner diffuser wall 523, or portions of the outer diffuser wall 524 may be joined to form the linear diffusion region 526. Likewise, portions of the inner diffuser wall 523, or portions of the outer diffuser wall 524 may be joined to form the turning region 527.

Moreover, each axial section forming the linear diffusion region 526 and the turning region 527 may be smoothly joined together, such that the linear diffusion region 526 coincides with a tangent of the turning region 527 at their interface. For example, the inner diffuser wall 523 may include a first surface of revolution about the diffuser axis 535, with the first surface of revolution including a first conic region and a first flared downstream portion 541. Likewise, the outer diffuser wall 524 may include a second surface of revolution about the diffuser axis 535, with the second surface of revolution including a smoothly joined second conic region and a second flared downstream portion 543 (the second flared downstream portion 543 as described further herein).

In addition, the inner diffuser wall 523 and the outer diffuser wall 524 may each be made from one or more components, or any combination thereof. In particular, the inner diffuser wall 523 and/or the outer diffuser wall 524 may be built up of a plurality of assembled sections. Moreover, each component or assembly may be manufactured differently and according to its shape or replaceablity.

For example, the inner diffuser wall 523 and/or the outer diffuser wall 524 may be made up of a plurality of assembled sections. Also for example, the inner diffuser wall 523 and the outer diffuser wall 524, including struts 525 may be made as an inlet unit 528 (e.g., a single cast part), with the remainder of the inner diffuser wall 523 and the outer diffuser wall 524 being a stacked assembly of annular wall sections. Also for example and as illustrated, the linear diffusion region 526 may built up as the inlet unit 528 and a stacked assembly of annular wall sections, and the turning region 527 may be made up of the first flared downstream portion 541 and the second flared downstream portion 543.

According to one embodiment, the exhaust diffuser 520 may be offset. In particular, the second flared downstream portion 543 may include a lower section 536 and an upper section 537 where the upper section 537 extends further downstream in an axial direction than the lower section 537, relative to the diffuser axis 535. Accordingly, and in contrast to a downstream tube end that is normal to the diffuser axis 535, here, the lower section 536 and an upper section 537 may terminate in an offset end 540. Note, the terms “upper section” and “lower section” are used for convenience to describe opposing sides of the second flared downstream portion 543 as illustrated in a vertical (0 degree) exhaust configuration, however other opposing sections are contemplated, particularly in exhaust systems having discharge directions other than 0 degrees. For example, in an application having a 90 degree discharge direction, the terms “upper section” and “lower section” could be replaced with “right section” and “left section”, respectively.

As illustrated, the offset end 540 may substantially define a truncation plane 549. The truncation plane 549 may form a cutback angle 546 with a normal plane 548, with the normal plane 548 being a plane normal to the diffuser axis 535. The cutback angle 546 may be approximately 2 degrees from the normal plane 548. Alternately, the cutback angle 546 may be between 1 degree and 5 degrees from the normal plane 548.

Similarly, the exhaust diffuser 520 may include an offset outer diffuser wall 524. In particular, the outer diffuser wall 524 may include a uniform section 538 and an offset extension 539, which together may encompass the lower section 536 and the upper section 537 described above. For example, the uniform section 538 may extend downstream from the diffuser inlet 521, and include a surface of revolution. The surface of revolution may be defined by a two-dimensional curve rotated about the diffuser axis 535, with the two-dimensional curve including a linear segment 526 and a curved segment. In addition, the offset extension 539 may extend downstream from the uniform section 538 to the diffuser exit 522, and include a truncated surface of revolution, terminating in the offset end 540 described above.

According to one embodiment, the exhaust diffuser 520 may include a “cutback” outer diffuser wall 524, for example in the second flared downstream portion 543, that is coordinated with the exhaust collector exit 551. In particular, the outer diffuser wall 524 may include a complex shape that may be conveniently described as a basic, “uncut”, shape having a downstream portion absent or “cutback”, the absent portion being predominantly located on the opposite side of, or substantially radially opposite from the exhaust collector exit 551.

Moreover, the basic, “uncut”, shape may be a surface of revolution about the center axis 95 and the “cutback” may include an oblique cut angle, relative to the center axis 95, such that it includes a maximum cutback 545 opposite the discharge direction 559. In addition, the surface of revolution about the center axis 95 may include both the linear diffusion region 526 and the turning region 527 described above.

For example the surface of revolution may be defined by a two-dimensional curve rotated about the center axis 95, the two-dimensional curve including linear segment and a curved segment, wherein the linear segment is aligned with a tangent of the curved segment. The linear segment and the curved segment may be shaped, oriented, and positioned to form a surface of revolution of both the linear diffusion region 526 and the turning region 527 described above for the outer diffuser wall 524.

The maximum cutback 545 is the point or portion of the outer diffuser wall 524 corresponding to the greatest absent portion, truncation, or “cutback” from the basic, “uncut”, shape. In particular, the outer diffuser wall 524 may have a single point (or several points where the cut is not planar) on its downstream end that is further from the downstream end of the basic, “uncut”, shape than all other downstream endpoints on the outer diffuser wall 524.

The maximum cutback 545 may be measured along a curve. For example, for each point on the outer diffuser wall 524 that forms part of the diffuser exit 522 (i.e., each point on the downstream end of the outer diffuser wall 524), a plane may be formed by the center axis 95 and the point. Accordingly, a curve corresponding to each point may be defined by the intersection of its respective plane and the basic, “uncut”, shape. The maximum cutback 545 may then be defined as the point (or portion) of the outer diffuser wall 524 that forms part of the diffuser exit 522 and has the longest extrapolation from the respective point on the diffuser exit 522 to the downstream end of the basic, “uncut”, shape along the in-plane curve.

The maximum cutback 545 may be measured along the center axis 95. For example, the maximum cutback 545 may include the point (or portion) of the outer diffuser wall 524 that forms part of the diffuser exit 522 and has the greatest axial distance from a reference plane that is normal to the center axis 95 and is located aft of the diffuser exit 522.

Alternately, the maximum cutback 545 may be measured along a radial 96. In particular, the maximum cutback 545 may include the point (or portion) of the outer diffuser wall 524 that forms part of the diffuser exit 522 and has the greatest radial distance from a point on the circumferential wall 553 along the same radial. Since the circumferential wall 553 may open up, or otherwise increase its radius as it approaches the discharge direction 559, this measurement of the maximum cutback 545 may be limited to a range of radials 96 greater than 180 degrees from the discharge direction 559.

According to one embodiment, the “cutback” of the outer diffuser wall 524 may be located in the second flared downstream portion 543. In particular, the second flared downstream portion 543 of the outer diffuser wall 524 may include an obliquely truncated shape. For example, the second flared downstream portion 543 may include a surface of revolution about the center axis 95 that is obliquely truncated proximate the diffuser exit 522, and further includes the maximum cutback 545 opposite the discharge direction 559.

To illustrate, the second flared downstream portion 543 may include an obliquely truncated trumpet bell shape having an obliquely cutback portion aligned substantially radially opposite from the exhaust collector exit 551. In particular, the obliquely truncated second flared downstream portion 543 may include a shape truncated from a basic, “uncut”, flared shape. The obliquely cutback portion generally refers to a surface of the second flared downstream portion 543 corresponding to the truncation or cut from an otherwise basic, “uncut” shape. The basic, “uncut”, flared shape is a flared surface of revolution, the surface being defined by a two-dimensional curve rotated about the center axis 95. In addition, the upstream end of the two-dimensional curve may be tangentially aligned to a line corresponding to the linear diffusion region 526 described above, thus forming the smooth transition at their interface.

As illustrated, the two-dimensional curve may substantially be quarter-circle (e.g., between 75 degrees and 105 degrees) having a flare radius 544, and oriented such that a radial 96 of center axis 95 runs tangential to the downstream end of the two-dimensional curve. Also as illustrated, the flare radius 544 may be constant up to the diffuser exit 522 (i.e., a terminating downstream end). Also, for reference, an extrapolation line 547 is shown, indicating a continuing flare radius of an absent portion of the two-dimensional curve at its maximum cutback 545.

Likewise, the two-dimensional curve may be made of other, non-circular curvatures. In particular, the two-dimensional curve may include a non-linear curve having an arc of approximately 90 degrees. For example the two-dimensional curve may have an arc between 75 degrees and 105 degrees. According to one embodiment, the flare radius 544 of the second flared downstream portion 543 may be concentric with a flare radius of the first flared downstream portion 541.

The obliquely truncated second flared downstream portion 543 may be described as the difference between the basic, “uncut”, flare shape and the truncation, absent portion, or “cutback” of the basic, “uncut”, flare shape. Here, the truncation includes the portion of the basic, “uncut”, flare shape between a normal plane 548 and a truncation plane 549.

The normal plane 548 is normal to the center axis 95, and defines the entire downstream end of the basic, “uncut”, flare shape. At least one point of the downstream end of the obliquely truncated second flared downstream portion 543 lies on the normal plane 548. The truncation plane 549 is normal to the flow symmetry plane, but is oblique to the normal plane 548 by a cutback angle 546. According to one embodiment, the cutback angle 546 may be less than 10 degrees from vertical. According to another embodiment, the cutback angle 546 may be between 1 degree and 5 degrees from vertical. According to another embodiment, the cutback angle 546 may be approximately 2 degrees from vertical. Alternately, the truncation may include the portion of the basic, “uncut”, flare shape between a normal plane 548 and a non-planar cutback.

The obliquely truncated second flared downstream portion 543 is truncated in coordination with the exhaust collector exit 551. In particular, the maximum cutback 545 of the obliquely truncated second flared downstream portion 543 is aligned with an exhaust collector turning region 555. The exhaust collector turning region 555 is generally defined as an area within the exhaust collector 550 that is opposite the discharge direction 559 where the exhaust gas 90 expelled from the diffuser exit 522 separated into opposing circumferential flows about the circumferential wall 553. For example, here, the exhaust collector turning region is at the bottom of the exhaust collector 550. Accordingly, here, the outer diffuser wall 524 includes a maximum cutback 545 or maximum truncation at its bottom end.

As above, the maximum cutback 545 is the point (or portion) of the outer diffuser wall 524 corresponding to the greatest truncation, absent portion, or “cutback” from the basic, “uncut”, flare shape, and may be measured along the center axis 95 and/or a radial 96. In addition, the maximum cutback 545 may be measured relative to its flare angle. In particular, the maximum cutback 545 may include the point (or portion) of the outer diffuser wall 524 that forms part of the diffuser exit 522 and has the shortest flare angle or arc. As described above, the second flared downstream portion 543 may be cut from a surface of revolution about the center axis 95. As such, the degree of flare is constant on the outer diffuser wall 524 at each axial location. Accordingly and for example, where the discharge direction 559 of the exhaust collector 550 is upward or 0 degrees from TDC, the flare shape at the top of the second flared downstream portion 543 may have a maximum arc (e.g., approximately 90 degrees), and the flare shape at the bottom of the second flared downstream portion 543 may have a minimum arc (e.g., approximately 50 degrees).

According to one embodiment, the inner diffuser wall 523 may be shaped similarly to the outer diffuser wall 524. In particular, the first flared downstream portion 541 may include a surface of revolution about the center axis 95 including a flare with between 75 degrees and 105 degrees of arc, and terminating in a substantially vertical direction at the diffuser exit 522. Moreover, the flare of the first flared downstream portion 541 may travel through approximately the same arc as the maximum arc of the second flared downstream portion 543. For example, the inner diffuser wall 523 may include a flare that is concentric with the flare radius 544 of the second flared downstream portion 543, shares approximately 90 degrees of arc with the second flared downstream portion 543 in a plane including the center axis 95 and a radial 96 in the discharge direction 559. In addition the downstream end of the inner diffuser wall 523 may be tangentially aligned to the aft wall 554, thus forming the smooth joint at their interface.

Furthermore, the inner diffuser wall 523 and the outer diffuser wall 524 may be offset from each other. In particular, the offset includes a substantially constant radial separation through their shared arc, as measured in the plane including the center axis 95. For example, the inner diffuser wall 523 and the outer diffuser wall 524 may be offset from each other through their shared arc by the length of the flare radius 544. Also for example, the inner diffuser wall 523 and the outer diffuser wall 524 may be offset from each other through their shared arc by the length of the flare radius 544 +/−25 percent.

According to one embodiment, the obliquely truncated second flared downstream portion 543 may be configured such that the maximum cutback 545 provides for a minimum gap 557 between the diffuser exit 522 at the maximum cutback 545 and the circumferential wall 553. In particular, the obliquely truncated second flared downstream portion 543 may be truncated so as to provide the minimum gap 557 between the outer diffuser wall 524 and the circumferential wall 553 of at least one half the distance between the inner diffuser wall 523 and the outer diffuser wall 524 at the diffuser exit 522, and as measured in a plane including the center axis 95 and a point on the maximum cutback 545. For example and as illustrated, where the circumferential wall 553 runs parallel with the center axis 95, the obliquely truncated second flared downstream portion 543 may be truncated such that the minimum gap 557 between the outer diffuser wall 524 and the circumferential wall 553 is measured along a radial 96 passing through the maximum cutback 545.

According to one embodiment, the exhaust collector 550 may include an “extended” exhaust collector turning region 555. In particular, the forward wall 552 may be configured such that a minimum axial distance 558 is maintained from the aft wall 554 within the exhaust collector turning region 555 and proximate the circumferential wall 553. For example, the minimum axial distance 558 may be at least four times the minimum gap 557. Also for example, the minimum axial distance 558 may be at least double a distance between the inner diffuser wall 523 and the outer diffuser wall 524 at the diffuser exit 522 measured in a plane including the center axis 95 and a point on the maximum cutback 545. Also for example, the minimum axial distance 558 may be approximately the same as an axial distance between the forward wall 552 and the aft wall 554 opposite exhaust collector turning region 555 and proximate the diffuser exit 522.

In the examples above, the forward wall 552 may be angled or non-vertical. For example the forward wall 552 may be angled so as to provide an expanding volume in the discharge direction 559. Alternately, forward wall 552 and the aft wall 554 may be substantially parallel to each other (e.g., both vertical) such that the minimum axial distance 558 is substantially uniform proximate the exhaust diffuser 520. Alternately, forward wall 552 may be substantially vertical.

INDUSTRIAL APPLICABILITY

The present disclosure generally applies to an exhaust system for a gas turbine engine, and a gas turbine engine having an exhaust diffuser. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine, but rather may be applied to stationary or motive gas turbine engines, or any variant thereof. As applied, gas turbine engines, and thus their components, may be suited for any number of industrial applications, such as, but not limited to, various aspects of the oil and natural gas industry (including include transmission, gathering, storage, withdrawal, and lifting of oil and natural gas), power generation industry, aerospace and transportation industry, to name a few examples.

Generally, embodiments of the presently disclosed exhaust system for a gas turbine engine are applicable to the use, operation, maintenance, repair, and improvement of gas turbine engines, and may be used in order to improve performance and efficiency, decrease maintenance and repair, and/or lower costs. In addition, embodiments of the presently disclosed exhaust system may be applicable at any stage of the gas turbine engine's life, from design to prototyping and first manufacture, and onward to end-of-life. Accordingly, the exhaust system may be used as a retrofit or enhancement to existing gas turbine engine, as a preventative measure, or even in response to an event. Moreover, the various combined features may be adapted to retrofit a previous design. This is particularly true as the presently disclosed exhaust system may be installed in a gas turbine engine having identical interfaces to another exhaust system so as to be interchangeable with an earlier type of exhaust system.

Gas turbine engines having exhaust collectors with a radial discharge direction may have an area of low flow at the opposite side of the exhaust collector exit (exhaust collector turning region) forward of the diffuser exit. Embodiments of the presently disclosed exhaust system may include and combine features, such as an offset or “cutback” outer diffuser wall that is coordinated with the exhaust collector exit, a flared inner diffuser wall, and an “extended” exhaust collector turning region to reduce the pressure at the turbine exit. Accordingly, the current disclosure provides an exhaust diffuser wherein the outer diffuser wall is cut back or radially extends less in the low flow area, relative to its radially extension in the discharge direction, thereby reducing its size and potential blockage within this turning region.

Use of the exhaust system as described above may result in increased turbine pressure ratio, leading to more shaft power and higher efficiency. In particular, through substantial analysis and empirical testing, the inventors have seen significant efficiency gains over previous designs. Accordingly, the combination of the aforementioned features, may provide for overall improved engine performance.

The preceding detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine. Hence, although the present embodiments are, for convenience of explanation, depicted and described as being implemented in a stationary gas turbine engine, it will be appreciated that it can be implemented in various other types of gas turbine engines, and in various other systems and environments. Furthermore, there is no intention to be bound by any theory presented in any preceding section. It is also understood that the illustrations may include exaggerated dimensions and graphical representation to better illustrate the referenced items shown, and are not consider limiting unless expressly stated as such. 

What is claimed is:
 1. An exhaust diffuser for a gas turbine engine, the exhaust diffuser comprising: a diffuser inlet; a diffuser exit; an inner diffuser wall including a first tubular member about a diffuser axis extending between the diffuser inlet and the diffuser exit, the first tubular member including a first flared downstream portion proximate the diffuser exit, and an outer diffuser wall including a second tubular member about the diffuser axis and at least partially about the inner diffuser wall and extending between the diffuser inlet and the diffuser exit, the outer diffuser wall and the inner diffuser wall forming a diffusing flowpath between the diffuser inlet and the diffuser exit, the second tubular member including a second flared downstream portion, the second flared downstream portion including a lower section, and an upper section, the upper section extending further downstream in an axial direction than the lower section, relative to the diffuser axis.
 2. The exhaust diffuser of claim 1, wherein the an outer diffuser wall further includes a uniform section extending downstream from the diffuser inlet, the uniform section including a surface of revolution, the surface of revolution defined by a two-dimensional curve rotated about the diffuser axis, the two-dimensional curve including a linear segment and a curved segment, and an offset extension extending downstream from the uniform section to the diffuser exit, the offset extension including a truncated surface of revolution terminating in an offset end, the offset end substantially defining a truncation plane (549), the truncation plane (549) forming a cutback angle (546) with a normal plane (548), the normal plane (548) normal to the diffuser axis, the cutback angle (546) between 1 degree and 5 degrees from the normal plane (548); and wherein the uniform section and the offset extension together encompass the lower section and the upper section.
 3. The exhaust diffuser of claim 1, wherein the first flared downstream portion extends radially outward from the diffuser axis, and includes a surface of revolution about the diffuser axis including a flare with between 75 degrees and 105 degrees of arc, the flare terminating in a substantially normal direction to the diffuser axis at the diffuser exit.
 4. The exhaust diffuser of claim 1, further comprising a plurality of diffuser struts circumferentially distributed around the diffuser axis and extending between the outer diffuser wall and the inner diffuser wall.
 5. An exhaust system for a gas turbine engine, the exhaust system comprising the exhaust diffuser of claim 1, and further comprising an exhaust collector configured to receive exhaust gas circumferentially from the diffuser exit, the exhaust collector including an exhaust collector exit located substantially opposite from the lower section, relative to the diffuser axis, a forward wall, an aft wall, and a circumferential wall extending between the forward wall and the aft wall, the circumferential wall encircling a majority of the diffuser exit.
 6. The exhaust system of claim 5, wherein the exhaust collector further includes an exhaust collector turning region opposite the discharge direction; and wherein the forward wall is maintained a minimum axial distance from the aft wall, the minimum axial distance being at least double a distance between the inner diffuser wall and the outer diffuser wall at the diffuser exit measured in a plane including the diffuser axis and a point on a maximum cutback of the lower section.
 7. The exhaust diffuser of claim 5, further comprising a minimum gap between the diffuser exit at a maximum cutback of the lower section and the circumferential wall, the minimum gap being at least one half a distance between the inner diffuser wall and the outer diffuser wall at the diffuser exit, and as measured in a plane including the diffuser axis and a point on the maximum cutback.
 8. The exhaust system of claim 5, wherein the gas turbine engine includes a center axis; and wherein the exhaust collector exit is configured to discharge the exhaust gas in a discharge direction radially between positive 135 degrees and negative 135 degrees around the center axis from top dead center, relative to the gas turbine engine.
 9. An exhaust system for a gas turbine engine, the exhaust system comprising: an exhaust diffuser including a diffuser inlet, a diffuser exit, an inner diffuser wall extending between the diffuser inlet and the diffuser exit, the inner diffuser wall defining a surface of revolution with a first flared downstream portion about a diffuser axis, and an outer diffuser wall extending between the diffuser inlet and the diffuser exit, the outer diffuser wall defining a truncated surface of revolution with a second flared downstream portion about the diffuser axis, the second flared downstream portion obliquely truncated proximate the diffuser exit and relative to a plane normal to the diffuser axis, the second flared downstream portion including a maximum cutback, the inner diffuser wall and the outer diffuser wall forming a diffusing flowpath between the diffuser inlet and the diffuser exit; and an exhaust collector including an exhaust collector exit configured to discharge exhaust gas along a discharge direction, the exhaust collector exit located substantially opposite from the maximum cutback, relative to the diffuser axis and along the discharge direction, a forward wall, an aft wall, and a circumferential wall extending between the forward wall and the aft wall, the circumferential wall encircling a majority of the diffuser exit.
 10. The exhaust system of claim 9, wherein the gas turbine engine includes a center axis; and wherein the exhaust collector exit is configured to discharge exhaust gas in a discharge direction radially between positive 90 degrees and negative 90 degrees around the center axis from top dead center, relative to the gas turbine engine.
 11. The exhaust system of claim 9, wherein the first flared downstream portion extends radially outward from the diffuser axis, and includes a flared surface of revolution about the diffuser axis including a flare with between 75 degrees and 105 degrees of arc, the flare terminating in a substantially vertical direction at the diffuser exit.
 12. The exhaust system of claim 9, wherein the exhaust collector further includes an exhaust collector turning region opposite the discharge direction; and wherein the forward wall is maintained a minimum axial distance from the aft wall, the minimum axial distance being at least double a distance between the inner diffuser wall and the outer diffuser wall at the diffuser exit measured in a plane including the diffuser axis and a point on the maximum cutback.
 13. The exhaust system of claim 9, further comprising a minimum gap between the diffuser exit at the maximum cutback and the circumferential wall, the minimum gap being at least one half a distance between the inner diffuser wall and the outer diffuser wall at the diffuser exit, and as measured in a plane including the diffuser axis and a point on the maximum cutback.
 14. The exhaust system of claim 9, wherein the exhaust collector further includes an exhaust collector turning region opposite the discharge direction; and wherein the forward wall is maintained a minimum axial distance from the aft wall, the minimum axial distance being approximately the same as an axial distance between the forward wall and the aft wall opposite the exhaust collector turning region and proximate the diffuser exit.
 15. The exhaust system of claim 9, wherein the truncated surface of revolution is at least partially defined by a two-dimensional curve rotated about the diffuser axis, the two-dimensional curve including linear segment at an upstream end and a curved segment at a downstream end, the linear segment aligned with a tangent of the curved segment at an interfacing point.
 16. An exhaust system for a gas turbine engine, the gas turbine engine having a center axis and a turbine, the exhaust system comprising: an exhaust diffuser including a diffuser inlet, a diffuser exit, an inner diffuser wall, and an outer diffuser wall, the inner diffuser wall, and the outer diffuser wall extending between the diffuser inlet and the diffuser exit and forming a diffusing flowpath therebetween, the diffuser inlet configured to axially receive exhaust gas from the turbine, the diffuser exit configured to radially discharge the exhaust gas, the inner diffuser wall including a first surface of revolution about the center axis, the first surface of revolution including a first conic region and a first flared downstream portion, the first flared downstream portion including a first flare radius, the outer diffuser wall including a second surface of revolution about the center axis, the second surface of revolution including a second conic region and a second flared downstream portion, the second flared downstream portion including a second flare radius and an cutback portion with a maximum cutback located substantially radially opposite from the exhaust collector exit; and an exhaust collector including an exhaust collector exit, a forward wall, a circumferential wall, and an aft wall, the circumferential wall extending between the forward wall and the aft wall, the exhaust collector configured to receive the exhaust gas circumferentially about the center axis from the diffuser exit, the exhaust collector exit configured to discharge the exhaust gas in a discharge direction radially between positive 135 degrees and negative 135 degrees around the center axis from top dead center, the discharge direction substantially radially opposite from the maximum cutback, relative to the center axis.
 17. The exhaust system of claim 16, wherein the first flared downstream portion extends radially outward from the center axis, and includes a flared surface of revolution about the center axis including a flare with between 75 degrees and 105 degrees of arc, the flare terminating in a substantially vertical direction at the diffuser exit.
 18. The exhaust system of claim 16, wherein the forward wall is substantially vertical.
 19. The exhaust system of claim 16, wherein the first flare radius and the second flare radius are concentric; and wherein the second flare radius is constant.
 20. The exhaust system of claim 16, wherein the discharge direction is radially between positive 5 degrees and negative 5 degrees around the center axis from top dead center. 